1. Field of the Invention
The invention pertains to the field of dry metallized film AC motor start and motor run capacitors and in particular to dry metallized polypropylene capacitors having a pressure sensitive fault interrupter.
2. Description of the Prior Art
There is virtually no known prior art either in printed literature or commercially available products in the area of dry metallized film capacitors having fault interrupters.
British Pat. No. 1,569,186 discloses a film capacitor in which a capacitor roll deforms when heated, breaking a contact. It is unclear whether a dry or wet capacitor is intended. The problem with this device is that by the time the internal temperature is high enough to deform the film roll, some other interruption would have occurred, such as an explosion.
U.S. Pat. No. 3,496,432 also pertains to a dry capacitor relying on temperature to break a contact.
U.S. Pat. No. 3,909,683 teaches a pressure sensitive fault interrupter in a dry film capacitor. It provides a yielding cavity with a fusible portion of one lead wire passing therethrough. In the event of over pressure caused by a fault, at least one contact bridge is separated. Unfortunately, gases can accumulate in the cavity and can be ignited by the breaking contact. Such a type of device tends to be unsafe for commercial use.
No dry film capacitors with fault interrupters are commercially available, indicating that the few devices disclosed in the patent literature having no commercial value, despite the proposed UL requirement in Capacitor-UL-810.
The literature on wet film capacitors with fault interrupters is extensive. Typical recent U.S. patents are numbers U.S. Pat. Nos. 4,398,782 and 4,454,561. In particular, U.S. Pat. No. 4,398,782 is an interrupter for a wet film multi-section AC capacitor in which a molded disc with ribs is utilized.